Trimming the seam allowance at a corner is the best way to make a sharp finished point. The little wedge of fabric removed from the seam allowance means less bulk so the corner is flat and sharp. Here's how to do it.

Stitch the seam, pivoting the stitching at the corner. Cut across the corner of the seam allowance, close to, but NOT through, the stitches.

Turn to right side. Use a chopstick or eraser end of a pencil to carefully push out the corner from the inside. (If you push too hard, you can make a hole in the corner.)

Press edges flat. The finished corner has less fabric inside and looks good from both sides.